With the development of magnetic sensor technologies, magnetic sensors have developed from early single-axis magnetic sensors to later double-axis magnetic sensors and then to current three-axis magnetic sensors, such that they can detect magnetic field signals in three directions X, Y and Z simultaneously.
For magnetic sensors such as AMR, GMR and TMR, a magnetic field sensing direction is in a plane of the thin film material, and measurement of X-axis and Y-axis magnetic field components in the plane may be implemented by making two sensors orthogonal, thereby implementing an XY two-axis magnetic field sensor system. However, for a Z-axis magnetic field component, the usual solution is building a discrete tilted single-axis plane magnetic sensor on a two-axis plane sensor, for example, the three-axis magnetic field sensor disclosed in the patent with Application No. 201110251902.9 and entitled “Three-Axis Magnetic Field Sensor”. However, this method has the following defects:
1) The X, Y two-axis magnetic sensor and the Z single-axis magnetic sensor are discrete elements before mounting, so that integrated manufacture of the three-axis magnetic sensor cannot be implemented, thereby increasing the complexity of the manufacturing process.
2) Compared to an integrated manufacturing method, positional precision of the elements of a three-axis magnetic sensor manufactured by assembling discrete elements are reduced, thus degrading the measurement precision of the sensor.
3) The sensing axis of the Z single-axis magnetic sensor is perpendicular to the X, Y two-axis magnetic sensor plane, and therefore, the dimension of the three-axis magnetic sensor in the Z direction is increased, thereby increasing the device size and the difficulty in packaging.
Another solution is using a slope to set a magnetic sensor unit to detect a magnetic signal in the Z direction, as disclosed in the patent CN202548308U entitled “Three-Axis Magnetic Sensor”. However, the slope angle in the sensor in this structure is hard to control, and shadowing effects are easily caused in the process of depositing a magnetoresistive thin film on the slope, thereby reducing the performance of a magnetic sensor element. Moreover, an algorithm is needed to calculate a magnetic signal in the Z-axis direction.
Another solution is a solution disclosed in the patent application 201310202801.1 entitled “A Three-Axis Digital Compass”, which converts a Z-axis magnetic field component perpendicular to a plane into a magnetic field component in an XY plane by using a distortion of the magnetic field by a flux concentrator, thereby implementing measurement on a magnetic signal in a Z-axis direction. However, the magnetic sensor of this structure needs an ASIC chip or computation using an algorithm to obtain magnetic signals in three X, Y and Z directions.
Currently, a three-axis magnetic sensor is manufactured mainly by methods such as etching a layer of a substrate to form a slope, depositing a magnetoresistive material thin film on the slope, and double deposition of the sensor material, for example, the manufacturing process of a sensor disclosed in the patent CN202548308U entitled “Three-Axis Magnetic Sensor” substantially includes etching a substrate layer of a wafer to form two slopes, double-depositing a magnetoresistive material thin film on the two slopes respectively, and conducting double annealing to manufacture sensor units for measuring in an XZ direction and a YZ direction. The European Patent Application EP 2267470 B1 also discloses a method for manufacturing a three-axis sensor, in which a substrate is etched to form a slope, and a sensor unit for measuring a magnetic field component in a Z-axis direction is manufactured on the slope. The angles of the etched slopes in the two implementations are hard to control, and there is a difficulty in depositing the magnetoresistive material thin film on the slope, which are not conducive to actual implementation. In addition, the patent application CN102918413A of the EVERSPIN TECHNOLOGIES INC. entitled “Process Integration of a Single Chip Three Axis Magnetic Field Sensor” also discloses a method for integrating a three-axis magnetic field, the method including: etching a first and a second plurality of trenches within a first dielectric layer, each trench of the first and second plurality of trenches having a bottom and a side; depositing a first material on at least the side of each of the first plurality of trenches, the first material having a high magnetic permeability; depositing a second material in the first plurality of trenches and depositing a third conductive material in the second plurality of trenches; depositing a second dielectric layer over the first dielectric layer and the first and second plurality of trenches; forming a first plurality of conductive channels passing through the second dielectric layer to the third material in a first portion of the second trenches; forming a first plurality of thin-film magnetoresistive magnetic field sensor elements on the second dielectric layer positioned adjacent to the sides of the first plurality of trenches, each one of the first plurality of thin-film magnetoresistive magnetic field sensor elements being electrically coupled to one of the first plurality of channels; and depositing a third dielectric layer over the second dielectric layer and the first plurality of thin-film magnetoresistive magnetic field sensor elements. This method is relatively complicated, and the operating process is not easy to control. In the prior art, the three-axis magnetic sensor may also be formed by using a flux concentrator, but magnetization directions of the pinned layers of its magnetoresistive elements are not aligned in the same direction rendering the implementation relatively difficult.